The past week or so on
Metafilter, Matt has had a note about registering to vote at the top of every comments page. You can disable the notice by clicking a link saying you're already registered—this sets a cookie to let the MeFi server know the note shouldn't be displayed for you anymore. It's very simple, and if ads are going to fund the web (grumble) why not try commercial
click-vanishing ads like this? I bet people would be willing to click on ads at sites they frequent if they know that doing so will make the ad disappear for a limited time. It would be easier for readers than blocking the image server, or using other technical tricks to defeat ads, advertisers could get more click-throughs, and both sides could acknowledge openly that ads are annoying. With click-vanishing ads I'd see them and think, "hmm, there's another ad. Better click it to get rid of it."